This past weekend my stock 05 800 HO Summit burned down on the PTO side. I had approx. 300 miles on new chrome rings. I was curious as to what happened so I pulled the head and found the top of the piston melted on exhaust side and the ring was broke. The cylinder wall is toast where the ring broke on the exhaust side. Mag side looked fine-plug color was good and wash was good. I really can't find anything wrong that should have caused this-intake looks sealed good and PTO seal looks good. It was rather cold the morning that this happened but I had carb heaters on. The sled was running fine and then it started loosing power and it would not idle. Carbs were clean and fuel was good 92 octane. I had noticed a wierd vibration in the engine at full throttle a couple days before the engine failure which makes me think that it had started to melt down long before the ring failed. Anyone have something like this happen? Did you have a problem getting it warranteed through Ski-Doo?